Quoted:
Regardless--it's bullshit.  

For those who know nothing--a tree is cut down and sawn into boards.  Those boards are cut to exact size--2"X4", 4"X4", etc.  They are then dried in a kiln to a certain percentage of moisture.  During this time they twist, warp, and crack.  The are then planed to dimensional size, which is what is sold--1 1/2" X 3 1/2" for a "2X4", etc.

It's been this way since transportation allowed such things to occur.  In the long past you went to a local (very local if using a horse-drawn wagon) and bought a full 2" X 4" "rough cut" board because that's what was available.  It wasn't dried and it ended up warping in most cases, especially if not nailed up immediately.  The "good old days" weren't exactly "good" in many ways.

Edit:  To further clarify, there is such a thing as "5/4 lumber"--pronounced "five quarter"--for instances where full dimension is needed.  It costs more, but is available.  It is rough cut to 2 1/4" X 4 1/4" then planed to a finished dimension of 2" X 4".  This is most often seen on deck boards, where you need a full 1" board in order to not need so much structure underneath.

Quoted:
I did not that.  Interesting.

I did know, since I was a little kid that 2x4's were actually 1.5"x3.5".